I. Field of the Invention
The invention is related to electronic control system for controlling the rate at which air and fuel are supplied to a heat engine and, in particular, to an air-fuel ratio optimization logic which optimizes the air-fuel ratio for the most efficient operation of the engine.
II. Description of the Prior Art
Various methods for controlling the operation of internal combustion engines are known in the art. Today, most of the engines in passenger cars are equipped with exhaust gas oxygen sensors which measure the partial pressure of oxygen in the exhaust. The electrical signals from these exhaust gas oxygen sensors are only indicative if the air-fuel ratio of the air-fuel mixture being supplied to the engine is either rich or lean with reference to a stoichiometric air-fuel ratio in which the air completely oxidizes the fuel leaving little or no oxygen residue. In most closed loop engine control systems, the air-fuel ratio of the air-fuel mixture being supplied to the engine is fairly near to the stoichiometric air-fuel ratio.
Other electronic engine control systems are known in the art which use other engine parameters for closing the loop from the engine to the electronic controller. L. Taplin in U.S. Pat. No. 3,789,816 teaches a lean burn system in which the air flow rate is held constant and the fuel rate is decremented until the engine vibrations reach a predetermined engine roughness. The fuel rate is then dithered to maintain the predetermined engine roughness. The engine roughness in Taplin's patent is measured by a vibration sensor attached to the engine.
C. K. Leung in U.S. Pat. No. 4,344,140 teaches an improvement to Taplin's engine control system in which the engine roughness is determined by measuring the instantaneous rotational velocity of the engine's flywheel. In the fuel control system taught by C. K. Leung, the roughness signal is used as a bias to maintain the engine roughness at a predetermined value.
In a like manner, Latsch in U.S. Pat. No. 4,161,162, Benachi et al in U.S. Pat. No. 4,172,433, and Frolenius in U.S. Pat. No. 4,140,083, all disclose engine control systems in which the fuel delivered to the engine is controlled or adjusted to maintain the fluctuations of the rotational speed of the engine's output at a predetermined value. In an alternate engine control system, Latsch in U.S. Pat. No. 4,064,846, an engine control variable, such as fuel, air or ignition timing is modulated and the phase of the resultant variation in crankshaft acceleration is used to adjust the magnitude of an engine control variable.